Does it need to work in flat mode or in file collections, or do you just want to copy the current path to the clipboard?
This button copies the current path to the clipboard:
<?xml version="1.0"?>
<button display="both" effect="gray">
<label>Copy Folder Path</label>
<icon1>AE-Icons\AEi-ClipFolder-20.png,0</icon1>
<function type="normal">
<instruction>runmode hide</instruction>
<instruction>SetClip.exe {sourcepath$|noterm}</instruction>
</function>
</button>
It uses my small SetClip program and the icon is from one of the AEon packs.
If you need the command to work in flat mode or in file collections then that would need a modifier to {filepath} which gets the parent directory. I can't see such a thing in the manual but such a thing seems useful so I'll file a feature request with GPSoft. For the time being, if you're desperate, it could be done with some VBScript.